The present invention relates to a nuclear magnetic resonance (hereinafter abbreviated as “NMR”) and an electron spin resonance (hereinafter abbreviated as “ESR”) antenna, and spectrometers using the same.
NMR and ESR apparatuses irradiate a sample placed under a static magnetic field with electromagnetic waves such as radio frequency waves, microwaves or the like, and receive a free induction decay signal generated from the sample to identify the structure of the sample.
In recent years, there have been developed a method of improving the receipt sensitivity using the principle of dynamic nuclear polarization (DNP), a microscope using an ESR apparatus, and the like. The DNP-based method of improving the receipt sensitivity employs an approach which polarizes electron spins of a solid-state sample at extremely low temperature using an ESR apparatus, and transfers the polarization of electron spins to nuclear spins for measurement by an NMR apparatus.
If an apparatus is capable of simultaneously measuring NMR and ESR, a sample need not be moved because an ESR apparatus is first used for polarization and then an NMR apparatus is used for measurement. Also, when a used ESR apparatus can capture images, information on the spectrum of a sample can be acquired by an NMR apparatus simultaneously while an image of the sample is captured by the ESR apparatus. In this way, the simultaneous NMR/ESR measurements can acquire much information such as information on the molecular structure, dynamics, and electronic state of the sample, though the apparatus is complicated as compared with a measurement of one of NMR and ESR.
For simultaneously measuring NMR and ESR, an antenna which supports resonance frequencies of both NMR and ESR is arranged for a sample placed in a magnetic field. Particularly, in a high magnetic field region in which the magnetic field is approximately seven tesla, the resulting ESR resonance frequency is as high as 196 GHz, which belongs to a field referred to as “high magnetic field ESR.”
A problem resulting from the formation of high magnetic field ESR is that difficulties are experienced in handling microwaves at 100 GHz or higher. Frequencies at 100 GHz or higher are hardly provided by commercially available standard frequency oscillation sources, and larger losses are produced in transmitting the microwaves through coaxial cables or waveguides. Other difficulties are encountered in designing an antenna for intensively irradiating a sample space with microwaves.
For implementing a high magnetic field ESR apparatus, a frequency source employs a GUNN oscillator, or its multiple-wave magnetron. A microwave is introduced into a magnet by using an oversized waveguide, or spatially propagating a microwave, which is quasi-optically formed into a Gaussian beam, for introduction into the magnet.
An antenna for forming a coupling with a sample may be made using a cylindrical cavity as described in J. Mag. Resonance, 140, 293-299 (1999), or a cavity referred to as “Fabry-Perot type” as described in Rev. Sci. Instrum. 69, 3924-3937 (1998). Also, a Fabry-Perot type cavity having a half mirror with a mesh formed on one side has already been implemented in a high magnetic field ESR apparatus for 200 GHz or higher (see Rev. Sci. Instrum. 70, 3681-3683 (1999).